I don't have any old stocks, only index funds, but if I had an investment I didn't want more of (old stocks) and another I did want more of (index funds), then I wouldn't be buying more of the investment I didn't want via dividend reinvestment, I'd be taking the dividends as cash and buying the investment I did want. There's nothing special about dividend reinvestment other than it happening automatically, so better to redirect that income to what you want to be buying.